The present invention relates to bail-type mine roof expansion anchors and, more particularly, to bail members of unique structure for holding the shell and camming plug of an expansion anchor in mutually assembled relation prior to installation.
For many years, one of the most widely used means of supporting and reinforcing rock structures such as mine roofs has been a mechanical expansion anchor having a hollow shell and tapered nut or camming plug held together by a bail. The shell structure is radially expanded into gripping contact with the wall of a drill hole in the rock by axial movement of the tapered camming plug into the shell. The plug is moved by rotation of a bolt in threaded engagement with a central bore in the plug. The bolt is rotated by a power wrench engaged with the bolt head outside the drill hole, and the bolt is tensioned by the wrench after the anchor is set.
Mining machinery in common use today may include a magazine holding a number of bolts with expansion anchors mounted thereon, and a movable boom structure carrying a power drill and wrench in addition to the magazine. A drill hole of appropriate diameter and depth is formed in the rock structure by the power drill. When the drill bit is extracted, the boom is moved laterally to position the bolter head, holding a bolt and anchor assembly taken from the magazine, under the entrance to the hole. The bolter head, which includes the wrench engaging the head of the bolt, is then advanced to insert the end of the bolt carrying the expansion anchor, into the drill hole. When the bolt is fully inserted, placing a bearing plate carried by the bolt head in engagement with the surface of the rock formation around the drill hole entrance, the bolt is rotated to set the anchor and tension the bolt.
In some applications, it is desirable to place a flowable grout or slurry in the drill hole, surrounding at least the upper end of the bolt and mechanical anchor. The grout subsequently hardens to enhance the strength and durability of the anchoring system. The grouting mix may be inserted after the mechanical anchor is installed by being pumped through a central bore extending through the bolt. In such cases, it is of course necessary that the bail or other anchor structure permit flow of the grout to the intended locations.
In the installation of mechanical anchors carried on the ends of bolts it is sometimes difficult to align the bolt with the drill hole opening and get the anchor inserted into the hole. This is particularly true when using the aforementioned, boom-type bolting machines. It is not uncommon for the drill opening, having a diameter of, e.g., 11/2"-2", to be 16 feet or more above the surface upon which the machine is supported. Thus, proper positioning of the boom may be extremely difficult.
It is a principal object of the present invention to provide a novel mine roof expansion anchor with means facilitating insertion of a bolt carrying the anchor on its threaded end into a blind drill hole in a mine roof, or the like.
Another object is to provide a bail member of novel and improved design which assists in the insertion of a mine roof expansion anchor assembly which includes the bail into the open end of a drill hole.
A further object is to provide a bail member, and expansion anchor assembly including such a bail member, which may be advantageously used in a mine roof anchoring system employing a bolt having a bore through which a hardenable grout or slurry is pumped into the drill hole.
Other objects will in part be obvious and will in part appear hereinafter.